The film will once more bring together Spinal Tap stars Michael McKean and Christopher Guest, who co-wrote and created the series. Other names who have figured in their films, such as Fred Willard and Don Lake, are also in the cast of the eight-part series.

It follows character Tom Chadwick, played by O'Dowd, who tries to unravel his family history after inheriting a box of belongings from a relative.

Guest - who created and scripted the show with British actor and writer Jim Piddock - is noted for his documentary-style, semi-improvised films.

Family Tree, a co-production with US firm HBO, is currently being made in the UK and it will be screened in the spring.

Irish star O'Dowd said: "I'm terribly excited and monumentally under-qualified to work on an improvised show with Chris Guest."

Guest joked: "Chris O'Dowd has been on my radar ever since he was a child actor in Wales."

BBC2 controller Janice Hadlow said: "I am delighted to welcome Christopher Guest to BBC television. It will be his first television series for British audiences and one I am proud to have here on the BBC."